More than 80% of samples were infected with an enterovirus, compared with just seven of 34 samples taken from healthy volunteers.

The study is published in the Journal of Clinical Pathology.

The findings raise the question of whether antiviral drug therapy would be beneficial

Dr Charles ShepherdM.E. Association

The finding may help explain why many patients with M.E. often have intermittent or persistent gut problems, including indigestion and irritable bowel syndrome.

Viral infections, such as Epstein Barr virus (glandular fever), cytomegalovirus, and parvovirus, are also known to produce many of the symptoms associated ME.

Enteroviruses, which infect the bowel, cause severe but short lasting respiratory and gut infections.

There are more than 70 different types, and they head for the central nervous system, heart and muscles.

The researchers found that in a significant proportion of patients the initial enteroviral infection had occurred many years earlier.

Drug possibility

They said: "Although finding a chronic infection of the stomach may not directly prove a similar infection in the brain, muscle or heart, it opens up a new direction in the research for this elusive disease."

Dr Charles Shepherd, medical adviser to the ME Association, said the study would re-open the debate into whether persistent viral infection plays a role in the condition.

He said: "We know from previous research that enteroviruses, the group of viruses being investigated in this study, can trigger ME/CFS in some people.

"There is also some evidence that enteroviral infection can then persist in various parts of the body including muscle and brain - a finding that could help to explain why muscle and brain symptoms are so characteristic of the illness.

"The new clearly adds weight to this theory. The findings also raise the question of whether antiviral drug therapy would be beneficial in this particular sub-group of ME/CFS patients."